Pulse graham crackers in a food processor until finely ground (there should be about 1/4 cup). Transfer to a small bowl; stir in coconut and set aside.

Using an electric mixer, beat butter and powdered sugar in a medium bowl until fluffy, 2–3 minutes. Add flour, vanilla, and salt. Mix just until dough begins to form. Fold in coconut-crumb mixture (dough will be soft and will hold together when pressed between your fingers).

Press dough evenly onto bottom of prepared dish (smooth surface with an offset spatula, if desired). Using a fork, prick dough all over.

Bake crust until golden brown and just set, 18–22 minutes. Set aside.

Lemon Curd

Cook egg yolks, eggs, sugar, lemon zest, and lemon juice in a medium saucepan over medium heat, whisking constantly and beating in as much air as possible (keeping the whisk moving prevents the curd from burning and the eggs from scrambling), until curd has thickened and begins to bubble, about 10 minutes. Remove immediately from heat.

Bake bars until center of filling is just set, 15–17 minutes. Transfer to a wire rack; let cool in pan for 30 minutes. Chill until cold, 2–3 hours. DO AHEAD: Lemon bars can be made 2 days ahead. Cover and keep chilled.